1. Field of the Invention
The present invention relates to a thermal printhead mounted on a thermal printer.
2. Description of the Related Art
FIG. 3 shows a conventional thermal printhead (see JP-A-H05-221002, for example). The illustrated thermal printhead X, including an elongated heating resistor 92 formed on a substrate 91, is connected with the thermal printer's control section Pr via a connector 96. The control section Pr sends signals necessary for performing the printing operation to a drive IC 93. The drive IC 93 has a strobe signal terminal 93a, to which a strobe signal is sent via a strobe signal terminal 96a of the connector 96. The strobe signal determines a duration of time for the heating resistor 92 to be energized. While the strobe signal assumes HIGH level, the drive IC 93 makes power application selectively to the heating resistor 92.
The substrate 91 is provided with a thermistor 94. The thermistor 94 is connected with the thermal printer's control section Pr via a thermistor terminal 96b of the connector 96. The control section Pr obtains information on the temperature of the substrate 91 based on a resistance value of the thermistor 94. If the thermistor 94 gives an extremely small resistance value (meaning that the substrate 91 is at an abnormally high temperature), the control section Pr stops sending the printing commands to the drive IC 93 in order to prevent the thermal printhead X from operating abnormally or being damaged.
However, there is still a risk that an unexpected malfunction occurs in the control section Pr, and the printing commands to the drive IC 93 fail to be stopped, even if the thermistor 94 gives an extremely small resistance value. In such a case, the thermal printhead X can be left in an abnormally heated condition for a long time.